Magnetic materials having rectangular hysteresis loops



April 1969 HIROSH! KITAGAWA ET AL 3,441,506

MAGNETIC MATERIALS HAVING RECTANGULAR HYSTERESIS LOOPS Filed Aug. 30, 1967 F heetz I of 9 FIG. I B Hm H Pb Hm 3 g 40 dVl LL? 2 g 8 IO 3 '5 0.8 w i u] 3 0.6 E

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MAGNETIC MATERIALS Wm RECTANGULAR HYSTERESIS LooPs I Filed Aug. 50, 1967 Sheet 3 of 9 F 1969 HIROSHI KITAGAWA ET AL r 3, ,506

MAGNETIC MATERIALS HAVING RECTANGULAR HYSTERESIS LOOPS Filed Aug. 30, 1967 v v s eet 4 of 9 l Mg0(m0l%) 38 MnO (mot FIG. 7

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I MAGNETIC MATERIALS HAVING RECTANGULAR BYSTERESIS LOOPS Filed Aug. .30, 1967 Sheet 5 of 9' SINTERING TEMPERATURE (*c) INVENTOg:

April 29, 1969 HIROSHI KI TAGAWA 5T M. 3,441,506

MAGNET IC MATERIALS HAVING RECTANGULAR HYSTERESIS LOOPS Filed Aug. 50, 1967 Sheet 7 of 9 PA CuO 5 moL% H CUO IOmoL% c 3 |2- f] NOTE= TEMPERATURE AND v es neRsspscfive Q to- 500C H cuRvEs slemw Tl-IOSEFORSINTERNG g A b/lzoo'c 3 6 200C g mom "00's hr 4hr a fl f 05 g v IVIIOOC os o 0.5

APPARENT DENSITY (9/cm FIG. ll

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-11 alumni medium April 29, 1969 H|RQ$H| TAg w ET AL 3,441,506

MAGNETIC MATERIALS HAVING RECTANGULAR HYSTERESIS LOOPS Filed Aug. 30, 1967 Sheet 9 of 9 i g FIG. l3 E w z 3- I 5:

3 3 S O o o s 0 as 3 5 ZnO (mol%) g g 5 QUANTITY OF H3 503 ADDED. weighm I .L. alwartl meahm' United States Patent 3,441,506 MAGNETIC MATERIALS HAVING RECTANGU- LAR HYSTERESIS LOOPS Hiroshi Kitagawa, Toshio Inoue, Susumu Kurokawa, and

Shinkichi Horigome, Tokyo-t0, Japan, assignors to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-to, Japan, a joint-stock company of Japan Continuation-impart of application Ser. No. 344,005, Feb. 11, 1964. This application Aug. 30, 1967, Ser. No. 664,488. Claims priority, application Japan, Feb. 12, 1963, 38/ 5,787 Int. Cl. C04b 35/38; H01f 1/34 US. Cl. 252--62.2 2 Claims ABSTRACT OF THE DISCLOSURE Magnetic materials most suitable for memory elements consists of 30-45 mol percent Fe O 10-50 mol percent MnO, 10-40 mol percent MgO, and CuO in an amount of from trace to 20 mol percent, or of such magnetic materials with further addition of ZnO in an amount of from trace to 15 mol percent. The magnetic materials possess rectangular hysteresis loops of short switching time, high signal-to-noise ratio, low required driving current.

This application is a continuation-in-part of our copending application Ser. No. 344,005 filed Feb. 11, 1964, entitled, Magnetic Materials Having Rectangular Hysteresis Loops, and now abandoned.

This invention relates to magnetic materials with rectangular hysteresis loops, and more particularly it relates to a new series of ferrites having rectangular hysteresis loops and having, furthermore, the unique combination of short switching time, high signal output voltage, high signal-to-noise ratio, and, moreover, low required driving current.

In general, the so-called ferrite cores with rectangular hysteresis loops are widely used as memory elements in large-capacity and high-speed electronic computers. Although the principal requirements for such ferrite cores to be used as memory cores for electronic computers are short switching time 1-,, high disturbed voltage a'v large signal'to-noise ratio S/N, and low driving current, Im, these requirements call for mutually conflicting characteristics. In terms of magnetism, these electrical requirements correspond to a high flux density B and a coercive force H which is substantially high. With respect to these requirements, the ferrites of the Mn-Cu and Cu-Mg series known heretofore have relatively small squareness ratios, and, because their 5/ N ratios are low as a memory characteristic for practical applications, it is difiicult to use these ferrites in actual practice. For this reason, ferrites of the Mn-Mg series have heretofore been used principally for such applications. However, even these ferrites have certain disadvantages as will be described hereinafter.

It is an object of the present invention to eliminate such disadvantages by providing a new series of ferrites having rectangular hysteresis and having, moreover, the unique combination of highly desirable characteristics as stated hereinbefore.

The foregoing objects and advantages as will presently become apparent have been achieved by the present invention, the specific nature and details of which will be best understood by reference to the following description, taken in conjunction with the accompanying drawings which are graphical representations, and in which:

FIG. 1 is a ternary diagram of ferrites of the Mn-Mg series;

FIG. 2 shows a rectangular hysteresis loop, presented for the purpose of defining the term squareness ratio;

FIG. 3 is a current-time diagram for describing pulses for measuring a ferrite characteristic used in this invention as one criterion of the suitability of the ferrite for memory cores;

FIG. 4 shows characteristic curves, obtained by the method indicated in FIG. 3, of a memory core according to the present invention;

FIG. 5 indicates the variation of memory characteristics due to variation in sintering time of a ferrite of the MnO-MgO-CuO series;

FIG. 6 is a ternary diagram of the system showing squareness ratios;

FIG. 7 are characteristic curves showing effects of MgO in the ferrite of MnO-MgO-CuO-Fe O series to be given to the memory characteristics;

FIG. 8 are characteristic curves showing elfects of sintering temperatures of the ferrite of series to be given to the memory characteristics;

FIG. 9 are characteristic curves showing relationships between the added quantity of CuO in the ferrite of MgO-ZnO-MnO-CuO-Fe O series and the apparent density thereof;

FIG. 10 are characteristic curves showing relationships between the apparent density of series ferrite and average crystal grain size thereof;

FIG. 11 are characteristic curves showing relationships among the crystal grain size, switching coefficient, and coercive force in the MgO-ZnO-MnO-CuO-Fe 0 series ferrite;

FIGS. 12 and 13 are, respectively, characteristic curves showing efiects of ZnO in the MgO-ZnO-MnO-Cu0-Fe O series ferrite to be given to the memory characteristics; and

FIG. 14 shows memory characteristics of the ferrite materials in case H BO is added.

Referring to FIG. 1, which is a ternary diagram of Mn-Mg series ferrites, the ferrites of compositional mol ratios within the limits of the area A have higher flux density B but lower coercive force H than those of mol ratios within the area Ba. For this reason, sintering ferrites of compositions within the area A at a temperature of from 1,300 to 1,400 degrees C., as practiced heretofore, merely affords miniaturization, but it has not been possible, by this practice, to produce ferrites which fully satisfy the requirements such as miniaturization and shortening of switching time of memory cores necessary for increasing the speeds and capacities of computers, and which can withstand actual use with high signal output voltage.

Accordingly, in order to obtain ferrites of miniature size and high flux density B and coercive force H attempts have been made, by utilizing the characteristic of high flux density of the ferrites corresponding to area A in FIG. 1, to control the grain size of the ferrite, through sintering temperature and time conditions, so as to increase the coercive force. In general, since the grain size becomes small when the sintering temperature is low, sintering ferrites of com-positions in the area A at low temperatures will cause increase in their coercive force. However, it has heretofore been difficult to cause the B-H loops of such ferrites to assume square shapes to the degrees of squareness necessary for operation of the said ferrites as memory cores.

3 The present invention contemplates overcoming the above described difliculties and providing ferrites of compositions which can be represented by the following formula:

.xFe O yMnO zMgO uCuO wZnO where:

Further, the ferrite material of the following compositional ratio is particularly excellent as the ferrite core for 1 the memory elements in respect to its squareness ratio, switching time, signal output voltage, signal-to-noise ratio, driving current, etc.

35 6x543 25 3 5 10 2 30 3544515 w l 0 By the method according to the present invention, a mixture of the above indicated composition is first presintered at a temperature in the range of from 800 to 1,000 degrees C., and the resulting product is ground to produce a powder. A suitable binder is added to this powder, and the mixture is pressed into a ring of the required size, which ring is then sintered in air at a temperature of from 1,100 to 1,400 degrees C. The ring is then slowly cooled from the sintering temperature to approximately 1,000 degrees C. and-is thereafter quenched. The above described sintering step may be alternatively carried out with the ring in a stream of nitrogen gas, in which case quenching is unnecessary, and slow cooling in the furnace is sufiicient.

The compositions and characteristics of examples of ferrites produced by the above described method of the invention are shown in Table 1. The specific conditions under which these samples were produced are: the sintering time of from 1 to 3 hours; the sintering atmosphere consisting of air; and the quenching medium consisting of air. Measurements of characteristics were carried out For the squareness ratio of a hysteresis loop, the value of determined from the magnetization curve as shown in FIG. 2 is generally used. The squareness ratio R in this case is a function of the driving field H and becomes a maximum at a certain value of H However, since this squareness ratio R is inadequate as a criterion by which to judge the suitability of'memory cores for electronic computers, the examples, in the present invention, were studied on the basis of a practical characteristic measured by using current pulses as indicated in FIG. 3 in addition to the squareness ratio.

More explicitly, measurements were made with a pulse width of 2.5 ,uSC., a pulse rise time of 0.1 sec and disturbed ratio (I /1 of 0.5. The pulse height, that is, the driving current I was varied and the signal output dv and the noise output (disturbed voltage zero) dv were respectively read with pulses A and B as shown in FIG. 3. The signal-to-noise ratio was represented by S/N= dv /dv By this measurement, a characteristic graph as shown in FIG. 4 was obtained. The values of the signal output dv the noise output av and the switching time T at the point in this graph where the noise output dv increases abruptly were taken as the characteristic value of each core.

FIG. 7 indicates the memory characteristics of the MnO-MgO-CuO-Fe O series ferrite in the case of its compositional ratios being 37-52 mol percent MnO, 4-19 mol percent MgO', 4 mol percent CuO, 40 mol percent Fe O In this case, as the added quantity of MgO increases, dv and S/N increase, and 1 decreases. I, also increases under the sintering conditions of the sintering temperature of 1,150 C., the sintering time of 2 hours, and the quenching by air. By increasing the sintering temperature as described hereinbelow, it will be possible to decrease the value of the driving current, although, in this case, the value of the switching time 7 becomes slightly larger. That is, as is apparent from the characteristic curves, presence of MgO in the ferrite material is effecat a temperature of 25 degrees C. on cores formed from 5 tive i improving the memofyfharacterisfic P The respective mixtures of the samples, each core being requlred mfimol'y charactenstlc can be Obtamed 1f the mils in its outer diameter, 20 mils in its inner diameter, Mgo Content ranges from 10 to 40 mol p when and between 6 and 7 mils in thickness. (In Table 1, dv the Mgo nten ec r n 4 mol p the denotes disturbed voltage zero or noise output, which 50 squareness ratio and S/N ratio become smaller, hence the will be descrlbed herelnafter.) ferrite material becomes impractical to use.

TABLE 1 Composition (mol percent) sintering F8203 M110 MgO ZnO CuO temp. 0.) Im (ma.) dvr (mv.) dvo (mv.) n 1 sec.) SIN 40 41 10 5 4 1,150 500 44 2 0.45 22 40 10 10 4 1,150 420 51 2 0.3 26 3s 23. 6 27 1. 4 5 1, 230 750 52 e 0. 4 7 36. 9 46. 2 10 2. 9 4. 0 1, 130 750 so 4 0. 3 20 31 25 0 4 1, 200 850 3 0.4 15 40 31 10 15 4 1, 150 320 44 3 0.35 15 40 43 13 0 4 1, 150 050 60 4 0. 4 15 40 40 10 0 10 1, 150 550 30 4 0. 7 9 38 23. 5 32 1. 4 5 1, 300 650 38 4 0. 55 7 40 31 10 15 4 1, 150 320 44 3 0. 35 14 40 1s 25 13 4 1,200 290 30 2 0.3 15 42 41 10 3 4 1, 150 650 34 2 0. 5 17 40 26 30 0 4 1,200 800 6 0. 35 8 40 20 30 s 2 1, 200 530 37 3 0. 12 4o 40 10 5 4 120 540 50 3 0. 4 20 No'rn.l'm denotes driving current; dvr denotes signal output voltage; dv denotes disturbed voltage zero; 1, denotes switching time; and S/N is signal-to-noise ratio.

Summarizing the measured characteristics of the examples shown in Table 1, driving current I of from 300 to 1,000 ma., signal output voltage dv of from 30 to 80 mv., switching time 1 20.3 sec and S/N 7 were obtained.

FIG. 8 shows effects of sintering temperature to be given to the memory characteristic of the ferrite materials of 38 mol percent, Fe O 27 mol percent MgO, 5 mol percent CuO, 28.6 mol percent MnO; and 1.4 mol percent ZnO sintered at various sintering temperature for two hours and airquenched. It will be seen from this graphical representation that, with increase in the sintering temperature, the value of I becomes smaller and 75 becomes larger. Concurrently, the signal-to-noise ratio varies. Accordingly, by changing the sintering temperature in accordance with the purpose for use, a required memory characteristic can be obtained.

In the following, further explanations will be made as to the effect of addition. of copper.

When cupric oxide (CuO) is added to the components of a composition in the area A of FIG. 1, the squareness ratio of the BH curve increases at a temperature of from 1,100 to 1,200 degrees C., and the ferrite produced therefrom can be operated as a memory element. For example, with the addition of CuO on the order of 4 mol percent, a ferrite having a signal output value dv of approximately 50 mv. and a switching time value 7 of approximately 0.4 sec. is obtained, wherefrom a 30-mil core having excellent characteristics can be produced. The only drawback is a driving current ll of 900 ma., which is slightly high. The effect derived from addition of copper is to enable the apparent density of the ferrite material to be increased at a same sintering temperature and sintering time as well as the average crystal grain size to be reduced, whereby the switching speed can be made slower.

FIG. 9 indicates relationships of the apparent density of the ferrite material having a composition represented y z aho ho )13.5 )36.5-x h Where 10:0, 4, and 10 mol percent, with respect to the sintering time in each case, the sintering temperature being 1,000 C., 1,100 C., 1,200 C., and 1,300 C. respectively. In each case, the apparent density can beimproved by the addition of copper, the effect of which is remarkable at the sintering temperature of 1,100 C. and 1,200 C.

FIG. 10 shows the relationship between the apparent density and the average crystal grain size of the ferrite material having the same composition as that of FIG. 9 above in relation to the sintering temperature and time, from which it is apparent that the addition of copper is effective to obtain ferrite materials of small average crystal grain size, andlarge apparent density. The apparent density of the material required as the memory core is approximately 4.5 g./ 0111.

FIG. 11 shows relationships of the crystal grain size, coercive force H and switching coefiicient Sw (SW=T AH-H where T5 is the switching speed, H is the external magnetic field, and H is the coercive force). It will be seen from the drawing that when the crystal grain size becomes larger, the coercive force H becomes small and the switching coeflicient increases. Accordingly, it will be apparent from FIG. 10 that presence of CuO is effective to obtain this kind of ferrite material having high switch speed and uniform crystal grain size, and improved apparent density. Further, the quantitative limitation of OuO to be added is determined by decrease in the squareness ratio of the BH curve, and the measured results thereof are shown in FIG. 6, which is a ternary diagram of squareness ratios R in case of a ferrite of 40 mol percent of Fe O sintered at l,200 C. for 2 hours and then quenched in air. From the graphical representation, it is found that the added quantity of CuO is desirably less than 20 mol percent. It has been found that when ZnO is added to the above-described components to cause a reduction in the coercive force H,, of the material itself and to cause, also, an increase in the flux density, the driving current 1 becomes lower. In a specific instance, by the addition of ZnO, a ferrite having a driving current 1. 2350 ma., an output voltage dv of 30 to 70 mv., a switching time 7 20.3 sec., and a signal-to-noise ratio S/Nz7 was obtained. The switching time of 03 p.566. obtained in this case has never been attained by ferrite materials known heretofore as far as the applicants are aware.

FIG. 12 is a graphical representation showing the memory characteristics of a ferrite material composed of 40 mol percent Fe O 10 mol percent MgO, 4 mol percent CuO, 0l7 mol percent ZnO, and 29-46 mol percent MnO which has been sintered at a sintering temperature of 1,150 C. for 2 hours and then air-quenched. As seen, the driving current 11 can be made smaller by adding ZnO. On the contrary, however, the S/N ratio is reduced and the switching time 1, becomes larger with increase in added quantity of ZnO. When the crystal grain size is made uniform, the coercive force H and the switching coefficient become smaller by addition of ZnO. FIG. 13 indicates this relationship, wherein the ferrite material composed of is sintered at a temperature of 1,150" C. for 2 hours and then air-quenched. The curves show that, when the driving current I is constant, it is possible to reduce the switching speed by the addition of Zn0.

As mentioned in the foregoing, if the ZnO constant is less than 15 mol percent, a desired object can be attained as is clearly shown in FIGS. 12 and 13. That is, when the ZnO content becomes more than 15 mol percent, the squareness of the hysteresis loop deteriorates and the S/N ratio is reduced, hence the ferrite material becomes unable to be utilized as the memory core.

It has been I found, furthermore, that in case ZnO alone is added without addition of CuO, sintering of more than 10 hours is necessary at a temperature as low as 1,100 to 1,250 degrees C. However, when CuO is added, the signal output dv attains its maximum value after sintering of 1 to 3 hours. One example is illustrated in FIG. 5 which indicates the memory characteristics in the case of a ferrite produced by sintering a mixture material composed of 40 mol percent of Fe O 4 6' mol percent of MnO, 10 mol percent of MgO, and 4 mol percent of CuO in air at 1,200 degrees C., then quenching the same.

Also, in the case of compositions within the area B in FIG. 1, it is possible, by adding ZnO and CuO and controlling the sintering temperature and time, to produce a 30-mil core having signal output voltage dv g50 mv. and switching time 7 20.4 #560. However, such cores produced from compositions within the said area B, have relatively high values of driving current I Still further, it has been found that by adding H BO' to the above-described mixture composition, it is possible to produce memory cores by a sintering process involving substantially low temperature and relatively short time. A specific example is illustrated in FIG. 14, which indicates the memory characteristics of a ferrite in the case wherein H BO is added to a material containing 40 mol percent of Fe O 46 mol percent of MnO, 10 mol percent of MgO, and 4 mol percent of CuO, and the resulting mixture is sintered in air at 1,100 degrees C. for 2 hours, then quenched. Even a material of such a composition that it cannot be used at all as memory core without the addition of H BO is rendered into a material exhibiting excellent characteristics by the addition of 0.02 percent by weight of H BO The proportion of this H BO added may be increased up to 0.5 percent by weight without adversely affecting the characteristics of the final product, and, although the driving current becomes high, it is possible to produce a memory core of short switching time and high output. Moreover, it is possible to obtain such a ferrite of a high squareness ratio through low temperature sintering.

While, in the foregoing examples, the description relates to 30-mil cores, it is, of course, possible to produce excellent memory cores by using materials of the abovedescribed compositions according to the invention for, for example, 12-mil, 20-mil, 50-mil and -mil cores, in addition to 30-mil cores.

As has been explained in the foregoing, the ferrite materials of Fe-Mn-Mg-Cu as well as Fe-Mn-Mg-Zn-Cu 7 8 series possesses short switching time, high signal output References Cited oltage, high signal-to-noise ratio, and low required driv- UNITED STATES PATENTS mg current, so that it is most suited as the ferrite core for the memory elements. Moreover, the ferrite material can g i b d dt lt'll tr t t d rownow e pro a re a we y OW sm 6 mg empera me an 5 3,188,290 6/1965 Dam et a1. 25262.62

for a short sintering time.

What we claim is: '1. A ferrite magnetic material having rectangular TOBIAS LEVOW Prlmary Exammer' hysteresis loop characteristics consisting essentially of R. D. EDMONDS, Assistant Examiner.

35-43 mol percent of Fe O 25-50 mol percent of MnO, 10

1030 mol percent of MgO, and 3-15 mol percent of US. Cl. X.R.

252-62 62 62. 4 t i 2. A ferrite material according to claim 1, further 6 4 added with ZnO in an amount of from trace to '10 mol percent. 5 

